The present disclosure generally relates to organic solar cells and similar electronic devices. Today's increasing demand for renewable energy resources, especially solar power, is driving researchers to develop low cost, efficient photovoltaic devices. Organic photovoltaics (OPVs) are an attractive route toward solving the terawatt energy problem.
Solution processed organic photovoltaics have the potential to become a low-cost photovoltaic technology. OPVs can be fabricated on flexible substrates in a roll-to-roll process, which may enable photovoltaics to enter entirely new markets. One of the milestones for commercialization of OPVs is improving device efficiencies, which reduces overall cost. One way of improving device efficiency is through utilizing interfacial charge transport layers.
Interfacial charge transport layers sandwich the photoactive layer and determine the device polarity, help to collect charges, and transport the charges to the electrodes. Materials for these charge transport layers can be transparent, have low resistance and be chemically stable. The electron transport layer collects and transports electrons mainly generated from the acceptor to the cathode. A low work function interface is required to make Ohmic contact with the organic photoactive layer. ZnO is a common n-type semiconductor used as an electron transport layer in OPVs. ZnO can be processed from a sol-gel solution, and when combined with post-annealing, produces crystalline thin films at low temperatures (150-200° C.). Tin oxide (SnOx) is known to be highly transparent and conductive but higher post-annealing at 350-500° C. is often required. In addition, SnOx has one of the lowest oxygen and water vapor transmission rates for metal oxides, which may aid in organic electronic device stability.
The low work function of ZnO and high conductivity of SnOx have been previously combined to form mixed metal oxides whereby the ratio of Zn:Sn affects the electronic and physical properties of composites. These zinc tin oxides have application in a number of areas including transistors, sensors, transparent conductors and organic photovoltaics.
There exists a need for a new low temperature sol-gel solution processing technique for preparing zinc tin oxides with tunable composition.